4 Answers
4

I use multifactor authentication with multiple Google accounts currently. To my understanding, ONLY if:

abc@gmail.com has xyz@gmail.com's password will abc@gmail.com be able to see the second page with the mulitfactor auth prompt

xyz@gmail.com tells abc@gmail.com that he isusing Multifactor Auth

Will abc@gmail.com be able to tell xyz@gmail.com is using Multifactor authentication.

Edit:
I just remembered one more way that abc@gmail.com would beable to know if xyz@gmail.com is using multifactor auth: If abc@myowngmail.com is a Google Apps administrator for @myowngmail.com, abc@myowngmail.com will be able to know wether @myowngmail.com is enabled to let users to enable multifactor on accounts under @myowngmail.com.

As you agree to their privacy policy it is entirely feasible that they would use that information about you to promote one of their products to a contact of yours, or someone that has you listed as a contact. Remember, they are in the business of selling.